Thermal spraying, also known as flame spraying, involves the heat softening of a heat fusible material such as metal or ceramic, and propelling the softened material in particulate form against a surface which is to be coated. The heated particles strike the surface where they are quenched and bonded thereto. A conventional thermal spray gun is used for the purpose of both heating and propelling the particles. In one type of thermal spray gun, the heat fusible material is supplied to the gun in powder form. Such powders are typically comprised of small particles, e.g., between 100 mesh U. S. Standard screen size (149 microns) and about 2 microns.
In certain instances it is highly desirable that a thermal spray gun produce a fan-shaped spray stream with an increased width. The purpose is to spray large areas quickly and with a minimum of waviness in thickness that may occur with ordinary, concentrated spray streams. Fan sprays would be particularly useful for producing corrosion resistant coatings which are typically on large areas, the coatings being, for example, of zinc, aluminum, or plastic. Another large-area application is for antifouling on pilings and ship hulls in sea water. It happens that these coating materials have relatively low melting points, so it is important that the thermal spray gun produce enough heat for heat softening or melting the powdered material being sprayed but not such as to oxidize or deteriorate it.
Several prior types of powder thermal spray guns have been known for producing fan sprays. For example, U.S. Pat. No. 4,192,460 (Matsuo) discloses a gun with a longitudinal row of holes for injecting powder between two other parallel rows of flame jets. This may produce a wide spray stream but is cumbersome, relatively inefficient and not as uniform a coater as may be desired.
U.S. Pat. No. 2,741,508 (Marantz) shows a broadened nozzle with a slotted orifice for propelling powder through an elongated ring of flame outlets. The nozzle is associated with a simple tubular assembly for feeding powder to the nozzle. This type of gun cannot, per se, deliver a very wide fan shaped spray stream, and does not provide control of temperature conditions for effective melting without overheating.
It also is possible to assemble several complete gun heads as taught in U.S. Pat. No. 3,028,257 (Svrchek et al) for spraying resins over extended areas. This, also, is cumbersome and susceptible to unevenness in coating thickness.
Therefore an object of the present invention is to provide a novel thermal spray gun for producing a fan-shaped spray stream. Another object is to provide a thermal spray stream for coating large areas with uniformity and efficiency. A further object is to provide a novel construction for a compact thermal spray gun producing a fan spray. Yet another object is to provide a thermal spray gun with a fan spray having controllable heating of spray powder.